Extracellular Synthesis of Silver Nanoparticles Using a Novel Bacterial Strain Kocuria rhizophila BR-1: Process Optimization and Evaluation of Antibacterial Activity

This article discusses the extracellular synthesis of silver nanoparticles (AgNPs) employing a bacterial strain of Kocuria sp. isolated from beverage industry wastewater. The isolated bacterial strain was discovered as Gram positive with a coccus shape and identified as Kocuria rhizophila BR-1 by standard molecular technique (16S rRNA) and biochemical tests. The occurrence of a dark brown colour in the solution and a surface plasmon resonance (SPR) peak at 405 nm indicates the existence of AgNPs. The nanoparticles are spherical in form, with a size distribution of 10–200 nm and mean particle size of 46.73 nm, according to transmission electron microscopy (TEM) and particle size distribution (PSD) analysis. The crystalline phase of the synthesised AgNPs was shown by X-ray diffraction (XRD) investigation. Maximum AgNPs production (1.281 absorbance units) was achieved at 9.89 pH, 54.07 °C temperature, 1.17 mM salt concentration, and 13.24 h incubation time. The antibacterial activity of the produced AgNPs against Salmonella typhimurium, Staphylococcus aureus , and Escherichia coli was found to be good. In this study, the Kocuria rhizophila BR-1 bacterial strain was used for the first time to synthesise AgNPs. Henceforth, the bacterial strain used in this study can be utilized for the efficient synthesis of silver nanoparticles. Graphical abstract